I am trying to compute what is the communication speed of Arduino Ethernet? The Ethernet board will be connected to PC via Ethernet port. I will send a data from PC and Arduino will return it to me and with that I will know how fast it is communicating. For my project, serial communication is too slow, that's why I am trying to do this. But, I am quite not sure how to do it? Any help....

The shield and the Arduino are communicating at about 4 Mbit/s. I guess in reality you could reach about 1 Mbit/s network traffic giving you roughly 100 kB/s data transfer rate, about 10 times what you get by a serial connection.

The Arduino Ethernet is basically an UNO with the Ethernet shield integrated on the board and the USB part removed. So there is no difference regarding your question.

You can check the speed yourself by programming a simple sketch that accepts a connection and returns every byte it receives. Then you have to write a benchmarking application on the PC side and let the two communicate. I don't know labview so I cannot give you hints there.

To my knowledge there is not existing code that does benchmark the speed of the Arduino Ethernet Shield. Theoretically you could just use the webserver example of the Ethernet shield and use web server benchmarking programs but you'll probably would get other results if you would do the same with direct socket programming.

If you wanna do the above google for "web server benchmark". You'll get lots of results, you have to decide which one is best for your case (there is no benchmark that can do that "in general").